Q4 LETTUCE, 
lettuce plant is yellowish green in color upon delivery, 
and the leaves are thin and brittle. The product should 
be wholly free from lice, or green-fly, and the tips of the 
leaves should show no tendency to wither or to turn 
brown. If heading lettuce is grown, the leaves should 
roll inward like cabbage leaves, and the heads should be 
compact and nearly globular and yellowish white towards 
the core (see Fig. 34, page 103). 
Temperature.— Lettuce must have a low temperature. 
The night temperature should not rise much above 45°, 
while it may go as low as 40°. The day temperature, in 
the shade, should be 55° to 65°. Lettuce which is kept 
too warm grows too tall, and the leaves are thin and 
flabby, and there is generally more danger of injury from 
aphis, rot and leaf-burn. In midwinter particular atten- 
tion must be given to ventilation, for if the air becomes 
damp and close, mildew or rot is almost sure to de- 
velop. In raising head lettuce, it is common to do the 
watering with tepid water just before heading, in order to 
accelerate the growth. 
Light.—Whilst a lettuce house must have an abun- 
dance of light, the plants do not suffer if they are some 
distance from the glass, and even if they receive little di- 
rect sunlight. The house should have an exposure to- 
wards the sun, and the framework ought to be as light as 
possible, if the best results are to be obtained; but dif- 
fused light is often as good as the direct burning rays of 
the sun. It should be said, however, that good lettuce 
may often be grown in heavy, rather dark houses, but 
more care is required (particularly in watering), the re- 
sults are less certain, and there is difficulty in growing the 
heading varieties to perfection. The electric light may 
also be used to advantage (see pages 80 and tor). 
Beds and benches.— Most of the commercial lettuce 
forcers prefer to grow the crop in solid or ground beds, 
where the temperature is cool and the conditions of 
